Distribution of calbindin-D28k immunoreactivity in the deep nuclei of the bottlenose dolphin (Tursiops truncatus) amygdaloid complex

The amygdala plays a key role in emotional learning and behavior. Calbindin-D28k (CB) is a calcium-binding protein located in a variety of neuronal cell types in many regions of the brain. Despite previous studies in rat (Kemppainen, J Comp Neurol 426, 2000) and Primates (Sorvari, Neuroscience 75, 1996), there are no reports concerning the distribution of CB immunoreactivity in the dolphin amygdala. Thus, we studied the distribution, morphology, and size of CB-immunoreactive (IR) neurons as well as the distribution of CB-IR neuropil in the deep nuclei of the bottlenose dolphin amygdala. The results obtained showed that in the deep nuclei CB-IR neurons were numerous and could be divided into two major cell types: pyramidal and onpyramidal neurons. Pyramidal cells were large, lightly stained and without an evident immunostained dendritic tree. Nonpyramidal neurons could be subdivided into three types on the basis on the shapes and sizes of their somata and on their dendritic morphology. Type 1 neurons had a small spheroidal somata from which arose thin primary dendrites. Type 2 neurons were large cells with angular somata and evident primary dendrites. Type 3 neurons had a fusiform somata originating the primary dendrites from their opposite pole. These data suggest that in the deep nuclei neuronal microcircuit activity is controlled also by different cell types that contain CB.